The present invention relates to a method of manufacturing an organic semi-conductor solid electrolytic capacitor in which a conductive polymer thin film layer of a heterocyclic compound is used as an electrolyte. More particularly, the present invention relates to a method of manufacturing an organic semi-conductor solid electrolytic capacitor which is characterized by the process for forming a conductive polymer thin film layer of a heterocyclic compound.
Conventionally, solid electrolytic capacitors use manganese dioxide (MnO.sub.2) or tetracyanoquinodimethane as a solid electrolyte. The conventional capacitors that use manganese dioxide (MnO.sub.2) or tetracyanoquinodimethane as a solid electrolyte are disadvantageous in that they involve very complicated and costly manufacturing processes, the specific resistance or ESR of the capacitors is high and there is a large leakage current.
Accordingly, in order to improve upon the aforementioned problems relating to these manufacturing processes and capacitor characteristics, a novel solid electrolytic capacitor has been proposed in which a polymer layer of a heterocyclic compound is used as the solid electrolyte For example, see the specifications of Japanese Patent Application Laid-Open Publication (KOKAI) Nos. 60-244017 and 61-2315 and Japanese Patent Application Number 62-86584.
In a solid electrolytic capacitor of this type, a polymer layer of a heterocyclic compound that is formed on the surface of a metal substrate having a dielectric oxide film formed thereon is used as a solid electrolyte. The polymer layer of a heterocyclic compound is formed by preparing an electrolytic solution which contains a heterocyclic compound, for example, pyrrole, and a boron compound, for example, ammonium borodisalicylate (ABS), as a supporting electrolyte in an organic solvent, for example, acetonitrile, dipping a metal substrate having a dielectric oxide film formed thereon into the electrolytic solution, and supplying a predetermined direct current using the metal substrate as an anode and the electrolytic solution as a cathode, thereby carrying out electrolytic oxidation polymerization, and thus forming a polymer thin film of a heterocyclic compound, for example, pyrrole, on the dielectric oxide film provided on the metal substrate.
Thus, the conventional polymer layer of a heterocyclic compound is formed by electrolytic oxidation polymerization carried out in an electrolytic solution which contains a heterocyclic compound and a boron compound as a supporting electrolyte in an organic solvent. However, if it is possible to form a high-quality polymer layer of a heterocyclic compound by use of not only the aforementioned electrolytic solution but also other electrolytic solutions, particularly one in which a compound other than a boron compound is employed as a supporting electrolyte, then the process for forming a polymer layer of a heterocyclic compound will be diversified and it will become possible to manufacture solid electrolytic capacitors having excellent capacitor characteristics even more efficiently. However, there has heretofore been no proper electrolytic solution other than the aforementioned one in which a boron compound is used as a supporting electrolyte.